fix(gemini): remove trailing slash from httpUrl to fix OAuth auth (#221) (#341)

The gemini-extension.json declared the MCP server URL as
"https://mcp.stripe.com/" (with trailing slash), while every other
config file in the repo (server.json, .mcp.json, providers/) and the
server's own OAuth Protected Resource Metadata all use
"https://mcp.stripe.com" (no trailing slash).

Per RFC 9728, the resource identifier in the OAuth protected resource
metadata MUST exactly match the URL the client uses to access the
resource. Gemini CLI constructs the "expected" resource from httpUrl,
so the trailing slash caused an exact-string mismatch:

  Protected resource https://mcp.stripe.com does not match expected https://mcp.stripe.com/

Removing the trailing slash makes the URL consistent with the server's
declared resource identifier and fixes the auth failure.

Fixes #221

gemini-extension.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "mcpServers": {
     "stripe": {
-      "httpUrl": "https://mcp.stripe.com/",
+      "httpUrl": "https://mcp.stripe.com",
       "oauth": {
         "enabled": true
       }